The present invention relates to an electric circuit arrangement for operating an unlatching actuator. The unlatching actuator may unlatch a door latch, in particular a vehicle door latch, more particularly a land vehicle door latch, such as a car passenger door.
Vehicle door latches with an electric control are known. International patent application number PCT/CA2004/001958 shows an electronic latch arrangement in which power from a main power source is used to unlatch vehicle doors via an unlatching actuator. In the event that the main power source becomes disconnected from the unlatching actuator (such as following a vehicle crash), the power required for unlatching is drawn from a back-up battery contained within the circuit. The circuit further includes a bank of capacitors connected between the main power source, the back-up battery and a motor which drives the unlatching actuator. Under normal conditions, the capacitors are charged by the main power source, and in the “emergency” condition (e.g., following a crash), the capacitors are charged by the back-up battery. Whenever unlatching is required, be it under normal or “emergency” conditions, the energy required by the motor to drive the unlatching actuator is provided by discharging the capacitors. In other words, the motor is directly connected to the capacitors, but is not directly connected to or directly powered by the main battery or the back-up battery. During the act of unlatching, energy is only ever drawn from the capacitor. During unlatching, no energy is drawn from the main power source or from the back-up battery. Power is only drawn from the main power source or from the back-up battery at times other than when unlatching is occurring. This is because it is not possible to simultaneously discharge the capacitor for unlatching and recharging.
The electronic circuit of PCT/CA2004/001958 further includes a microcontroller which controls the components of the circuit, as well as receiving signals from the inside and outside door handles of the vehicle, for example. Under normal conditions, the microcontroller draws a current from the main power source. Under “emergency” conditions, the microcontroller continues to draw a current, initially from the capacitors, and then from a regulator. The microcontroller is therefore operational under both normal and “emergency” conditions and is thus safety critical. If, as a result of a vehicle crash, the microcontroller is damaged and rendered inoperative, it will not be possible to electrically release the doors because the release signal (as generated by operating either the inside door handle or the outside door handle) is transmitted via the microcontroller.